Quick Start Internet Protocol

Quick Start Internet Protocol.

　　We've all heard about Internet protocols, what are Internet protocols?

　　The core of the Internet is a series of protocols called Internet Protocol (Internet protocal Suite). Internet protocols can be broadly divided into five tiers.

1. Application tier (Application layer)

2. Transport layer (Transport layers)

3. Network layer

4. Link Layer

5. Physical layers (physical layer)

First of all, let's take the following points:

• The closer the layer is to the user, the closer the layer to the lower the hardware.
• Each layer is designed to accomplish a specific function, and in order to implement these functions, you need to abide by the same protocol.
• Every layer of the Internet has many agreements, collectively known as Internet protocols.

Part I: Physical layer

As we've just said, the closer the layer is to the hardware, here's the way. the physical layer is the physics that connects the computer. we know that if a computer is to be networked, we need to link the computers with optical cables, cables, twisted pairs, radio waves and so on. This is the physical layer. Its main function is responsible for transmitting 0 and 1 of electrical signals.

Part II: Link Layer

　A. Clearly, the task performed by the physical layer alone (the transmission of electrical signals of 0 and 1) is meaningless. The role of the link layer is to group the electrical signals 0 and 1, so that the electrical signal will be meaningful. There are many protocols for determining how to group, and the Ethernet protocol is a very popular protocol. It stipulates that each group of signals 0 and 1 is composed of a packet , also called a frame, each packet (frame) consists of two parts, the header (head) and the data.

For data packets, there are a few things to note:

• "header" Contains some description items for the packet, such as sender, receiver, data type, and so on.
• "Data" is the specific content of the packet.
• The header length is fixed at 18 bytes with a minimum data length of 46 bytes and a maximum of 1500 bytes.

　　B . MAC address. In a we refer to the data packets (frames) specified by the Ethernet protocol, with headers and data, the recipients and senders in the header, so how are the receivers and senders identified? Ethernet Rules: All devices connected to the network must have a NIC interface , and the packet (frame) must be routed from one network card to another. and the network card in the device is the address, the network card address is the sending address of the packet and the receiving address, we become the MAC address .

For Mac addresses, here are a few things to note:

• Each NIC address comes with a unique MAC address in the world, just like everyone in China has a different ID number.
• The length of a MAC address is 48 binary numbers, which are represented by 12 hexadecimal digits (for convenience).
• The first 6 bits of the MAC address are the vendor number, and the last 6 bits are the NIC serial number.

　　C. Broadcasting. NOTE: Ethernet packets must know the receiver's MAC address to send, but even with the receiver's MAC address, how to send it? The Ethernet protocol stipulates that broadcasting is used-that is, not sending packets to the receiver accurately, but broadcasting the packet to all computers on the local network, so that each computer makes its own judgment to see if it is the receiver.

When the sender sends the packet to all computers in the network, each computer reads the MAC address of the receiver in the header and compares it to its MAC address, and if it is the same, it is discarded if it is different.

Part III: Network layer

A. Why is there A network layer?

The Ethernet protocol disadvantage has two. One: the transmission of Ethernet packets by means of broadcast, which causes the local network computer to receive each, making it inefficient and resource-intensive. Second: The broadcast is confined to the sub-network where the sender is located , for the two cities that are far away, they must not be in the same sub-network, so, at this time, the Ethernet packet will not be sent out and received. It's also good to be confined to a sub-network, because if you send the packet to every computer in the world, it's going to be a devastating disaster!

　Based on this reality, we need a way to determine which MAC addresses belong to the same network, which MAC addresses are not part of the same network, and address the problem of not sending packets to a network outside the sender's sub-network.

At this time, the network layer came into being, it introduced a different from the MAC address of the new address, this set of addresses called " Network Address " (abbreviated URL). Url

Quick Start Internet Protocol